JP3396442B2 - Sludge treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electroplating tin, and more particularly to a method for treating sludge inevitably produced by halogen electroplating.

[0002]

2. Description of the Related Art The halogen method is one of the continuous methods for producing electroplated tin steel sheets. This uses a halogen bath containing stannous chloride, sodium chloride, sodium fluoride, and sodium hydrogen fluoride as a plating solution, electrolyzes metal tin as an anode, and a running steel plate as a cathode to make metal tin the steel plate surface. It is an electroplating method of electrodepositing on.

This halogen method is convenient for eluting the metallic tin of the anode as tin effective for plating into the electrolytic solution because the electrolytic solution (plating solution) used is acidic, but divalent tin is dissolved. The reaction of being oxidized by oxygen to form tetravalent tin also proceeds at the same time, and a large amount of sludge is generated. The main component of this sludge is sodium fluorostannate represented by Na ₂ SnF ₆ . In addition, due to iron ions eluted from the steel plate
A small amount of sodium fluoroferrate represented by Na ₃ FeF ₆ is also formed.

As another factor of sludge generation,
There are divalent iron ions eluted from the steel sheet into the plating solution.
The halogen method can operate at a high current density and is suitable for a high-speed line, but the bath is agitated by running the steel sheet at a high speed, and air is taken into the plating solution.
Alternatively, when the plating solution is circulated, air is taken into the plating solution. The divalent iron ions are oxidized by the oxygen thus dissolved in the plating solution to become trivalent iron ions. When the trivalent iron ions are reduced to divalent iron ions in the plating solution, the divalent tin ions are oxidized to tetravalent tin ions, so that sludge is generated. In order to prevent such oxidation of divalent tin ions,
It is common practice to add sodium ferrocyanide Na ₄ Fe (CN) ₆ to combine with iron ions and precipitate as iron ferrocyanide Fe ₄ [Fe (CN) ₆ ] ₃ to form sludge. ing.

Therefore, when the steel sheet is tin-plated by the halogen method electric tin plating, sludge containing cyanide, fluoride and the like is produced in the plating bath. If this sludge increases during the operation, it will hinder the operation. Therefore, the operation equipment was regularly stopped and the sludge was taken out of the bath. The sludge that was taken out contains tin as a valuable metal,
As a method for recovering metallic tin, for example, Japanese Patent Application Laid-Open No. 57-70242 discloses a method for recovering metallic tin from a halogen bath tin plating sludge as shown in FIG. In this method, sludge is made into a slurry form, and after adding this slurry to hot alkali (NaOH), it is filtered to separate sludge containing a large amount of iron (hereinafter also referred to as blue sludge), and the resulting filtrate is provided with acid. In addition, the pH is adjusted to 7-13, electrolysis is performed, and tin is electrodeposited and recovered.

However, in the method described in Japanese Patent Laid-Open No. 57-70242, harmful substances such as cyan in blue sludge are left undetoxified, and in the treatment of adding the slurry to hot alkali (NaOH). Since Sn also precipitates with Fe, there was a problem that the Sn concentration in the filtrate was lowered and the amount of tin finally recovered was reduced. In addition, the price of tin bullion has fallen, and the cost of smelting has exceeded the price of tin bullion that can be obtained by recovery, and the recovery of metallic tin from sludge is becoming less economical. However, since sludge contains cyanide and fluorine, it is necessary to remove or detoxify these elements so as to be less than the regulated value in the case of industrial waste.

In response to such a problem, Japanese Patent Application Laid-Open No. 9-103790 discloses a tin-plated sludge in which sludge is leached with water and filtered, and the remaining blue sludge is subjected to thermal hydrolysis treatment in the presence of calcium ions. And / or sludge containing an oxidizing agent in a sludge-containing liquid under conditions of pH 5.5 to 6 and subjected to water leaching treatment and then filtration to adjust the pH of the filtrate to 7.5 to 7. There is disclosed a method for treating tin-plated sludge in which tin hydroxide and tin oxide are adjusted to 9.0 and the separated precipitate (hereinafter referred to as tin-based sludge or white sludge) is reduced to metallic tin. As a method of recovering metallic tin from the separated precipitate, a molten salt electrolysis method or a method of melting with graphite and separating iron by the melting point difference,
A reduction dissolution method for tapping is disclosed.

Further, Japanese Patent Application Laid-Open No. 9-67699 proposes a device for realizing a processing flow for processing sludge as shown in FIG. The apparatus is a sludge decomposing device that separates sludge into an aqueous solution containing divalent tin ions and a solid content, a white sludge processing device that performs processing for recovering metallic tin from the aqueous solution, and the solid content as industrial waste. It is an apparatus for producing an electric tin steel plate by a halogen method, which is provided with a blue sludge treatment apparatus for treating the same. In the technique described in Japanese Patent Laid-Open No. 9-67699, NaOH is added to an aqueous solution containing divalent tin ions.
Was added to the white sludge containing SnO ₂ · nH ₂ O as a main component, and a carbon-based reducing agent was added to the metal sludge to heat it to reduce and dissolve the metallic tin, and to separate the iron content due to the difference in melting point, and then to release the hot water. Metal tin is recovered by casting.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the technique described in Japanese Patent Publication No. 90, a molten salt electrolysis method or a reduction dissolution method is used to recover metallic tin.
In addition to the problem that dust is generated and the working environment is deteriorated because all of them are dry reductions, the melting point fluctuates depending on the iron content in the separated precipitate, and it is very difficult to control the temperature and control the reduction reaction. However, there is a problem that the purity of tin is lowered and the recovery rate of tin is lowered. In addition, JP-A-9-67699
In the technique described in Japanese Patent Publication No. 9-103790, the iron component is separated by the melting point difference when the white sludge is heated and reduced and dissolved to obtain metallic tin.
It had problems of deterioration of working environment and reduction of tin recovery rate.

In view of the above situation, it is an object of the present invention to provide a method for treating halogen-type electric tin plating sludge, which has a high recovery rate of metallic tin and does not deteriorate the working environment.

[0011]

[Means for Solving the Problems] As described above, the sludge unavoidably generated when the metal tin is electroplated on the steel sheet by the halogen method electrotin plating is fluorinated represented by Na ₂ SnF ₆ . It contains sodium stannate, sodium ferrofluoride represented by Na ₃ FeF ₆ , and iron ferrocyanide represented by Fe ₄ [Fe (CN) ₆ ] ₃ as main components.

The inventors of the present invention have earnestly studied a sludge treatment method capable of effectively utilizing the resources contained in the sludge, particularly a sludge treatment method capable of recovering metallic tin at a high recovery rate. This sludge is leached with warm water to transfer sodium fluorostannate Na ₂ SnF ₆ into the aqueous solution, and then sodium fluoroferrate Na ₃ FeF ₆ and iron ferrocyanide Fe ₄ [Fe (CN) ₆ ] ₃ as a precipitate, and then solid-liquid separation is performed to obtain a filtrate containing sodium fluorostannate Na ₂ SnF ₆ and sodium fluoride NaF, and sodium ferrofluoride Na ₃ Fe.
It is separated into solids containing F ₆ and iron ferrocyanide Fe ₄ [Fe (CN) ₆ ] ₃ .

The filtrate containing sodium fluorostannate Na ₂ SnF ₆ and sodium fluoride NaF is first pH-adjusted and separated into a solid content containing tin and a filtrate. First, the present inventors
The conditions for water leaching and the reduction conditions for tin-containing solids were examined.As a result, the amount of Sn transferred to the aqueous solution was increased, and the tin-containing solids obtained were dissolved in alkali and electrolytically reduced in an alkaline aqueous solution. Therefore, it was found that it is not necessary to consider the adverse effect of the iron content contained in the tin-containing solid content, and the recovered metal tin has a high purity and a high metal tin recovery rate.

That is, the present invention is a method for treating sludge generated during electroplating of metal tin on a steel sheet by halogen method electrotin plating, wherein the sludge has a pH of 1.
After the water leach in the range from 0 to less than 4, subjected to solid-liquid separation process, and the obtained filtrate was pH adjusted, subjected to solid-liquid separation process, subjected to alkaline lysis process resulting solids ,
Then a sludge processing method characterized by recovering metallic tin performs electrolytic reduction treatment the alkali dissolution treatment solution as an electrolyte solution, the present invention, pH adjusters before Symbol resulting filtrate, the pH 7 to 9 It is preferable that the alkali dissolution treatment is performed by adding an aqueous sodium hydroxide solution.

Further, in the present invention, the electrolytic reduction treatment is
The Sn concentration in the electrolytic solution is preferably in the range of 20 to 45 g / l. The recovered metallic tin can be reused as an anode for plating treatment, and the filtrate from which tin-containing solids have been separated can be reused as a plating solution source.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A sludge treatment flow suitable for carrying out the present invention is shown in FIG. In the present invention, the sludge generated during the electroplating of the steel sheet with the metal tin by the halogen method electrotin plating is first subjected to the water leaching treatment. In the water leaching treatment, 5 to 15 times the amount of warm water is added to the sludge in the reaction tank, and the sludge is slurried by stirring. As a result, sodium fluorostannate Na ₂ SnF ₆ in the sludge migrates into the aqueous solution, and other sodium ferrofluoride Na ₃ FeF ₆ and iron ferrocyanide Fe ₄ [Fe (CN) ₆ ] ₃ precipitate. It remains in the solid content as a substance. The hot water used for water leaching is 50 to 70
C is preferred. In addition, it is preferable that the sludge is put into a high-speed stirring tank and stirred in advance before leaching with water.

The water leaching treatment is carried out in the range of pH less than 4 and 1.0 or more . When the water leaching treatment is carried out in the range of less than pH 4 and 1.0 or more, the amount of Sn transferred into the liquid increases and the recovery rate of Sn from the filtrate improves. When the pH is 4 or more, the amount of iron ions mixed into the liquid is reduced, but the amount of Sn transferred into the liquid is reduced. Further, in the water leaching treatment, to promote the oxidation of Fe ²⁺ ions, to be present as Fe ³⁺ , in order to suppress the transfer of Fe into the liquid, H ₂ O ₂ ,
It is preferable to add an oxidizing agent such as O ₂ or NaClO ₄ .

The sludge-containing treatment liquid that has been subjected to the water leaching treatment is then subjected to a solid-liquid separation treatment to separate it into a solid content and a filtrate. The solid-liquid separation treatment is preferably filtration using a filter, but it is particularly preferable to use a filter press which facilitates solid-liquid separation. The filtrate obtained by the solid-liquid separation treatment after the water leaching treatment mainly contains sodium fluorostannate Na ₂ SnF ₆ and sodium fluoride NaF ₂ . In the present invention, the pH of this filtrate is adjusted to precipitate tin in the filtrate as tin hydroxide.

The pH of the filtrate is adjusted by adding an alkaline aqueous solution. As the alkaline aqueous solution, a NaOH aqueous solution, a KOH aqueous solution, a LiOH aqueous solution, an NH ₄ OH aqueous solution and the like are suitable. The pH of the filtrate is preferably 7-9. If the pH of the filtrate is out of this range, the tin recovery rate will decrease. Under this condition, when Na ₂ SnF ₆ in the filtrate is used as the alkaline aqueous solution, the reaction solution represented by the following formula (1) causes Sn ₂ SnF ₆
H) ₄ (SnO ₂ · 2H ₂ O) precipitates.

Na ₂ SnF ₆ + 4NaOH → 6NaF + Sn (OH) ₄ ↓ (1) To adjust the pH of this filtrate, put the filtrate into a reaction tank separately installed, and further add sodium hydroxide aqueous solution etc. to this reaction tank. It is preferable to add the alkaline aqueous solution of.
Needless to say, stirring may be carried out in the reaction tank to promote the reaction.

The above-mentioned filtrate containing the precipitate is then transferred to a filter press or the like and subjected to solid-liquid separation to obtain a tin-containing solid content.
It is separated into a filtrate containing NaF 2. The filtrate containing NaF 3 is recovered and used as a plating solution source. An aqueous alkali solution is added to the tin-containing solid content, and an alkali dissolution treatment is performed.
The alkaline aqueous solution to be added is not particularly limited as long as [OH ⁻ ] ions are generated, but NaOH aqueous solution, KOH aqueous solution, LiOH aqueous solution, NH ₄ OH aqueous solution and the like are preferable.

By the alkali dissolution treatment, tin hydroxide Sn (OH)
₄ reacts with the added alkali and dissolves in the aqueous solution in the state of SnO ₃ ²⁻ . The reaction is shown in the following formula (2) when a NaOH aqueous solution is used as the alkaline aqueous solution. Sn (O
H) ₄ becomes sodium stannate Na ₂ SnO ₃ and dissolves in the aqueous solution. The amount of the alkaline aqueous solution to be added is preferably equal to or more than the equivalent in the reaction of the formula (2).

Sn (OH) ₄ + 2NaOH → Na ₂ SnO ₃ + 3H ₂ O (2) In the alkali dissolution treatment, the tin-containing solid content is put into a separately installed dissolution tank, and an alkaline aqueous solution is further added to tin. It is preferable to dissolve the tin contained in the solid content in the aqueous solution. In addition,
Needless to say, the dissolution tank may be stirred or heated to an appropriate temperature to accelerate the reaction.

Further, in the alkali dissolution treatment, a trace amount of Fe content remaining in the tin-containing solid content is not dissolved in the aqueous solution but settles as a precipitate. Therefore, it is possible to reduce the iron concentration in the alkali solution, which has the remarkable effect of improving the purity of metal tin recovered in the electrolytic reduction treatment in the next step and improving the recovery rate of metal tin. . Also, by adopting the alkali dissolution treatment, it is not necessary to reduce the concentration of iron that migrates in the filtrate during the water leaching process, and the amount of tin that migrates from the sludge into the filtrate can be increased. There is also an effect that the recovery rate is improved.

Next, electrolytic reduction treatment is carried out by using the above-mentioned alkaline dissolution treatment liquid in which Sn is dissolved as an electrolytic solution, and metal tin is electrodeposited to recover metal tin. The reaction in the electrolytic reduction treatment is shown in the following formula (3). _{^{Cathode: SnO 3 2- + 4e - +}} H 2 O → Sn 0 + 6OH - ...... (3a) _{^{anode: 4 OH - → 2H 2 O}} + O 2 ↑ + 4e - In the electrolytic reduction treatment in the present invention ...... (3b) is , Sn in electrolyte
It is preferable to adjust the concentration to 20 to 45 g / l and perform electrolytic treatment from the viewpoint of increasing the reduction rate of tin.

The reduction efficiency in the electrolytic reduction treatment is represented by cathode efficiency, cathode efficiency (%) = {(actual tin reduction amount) / (theoretical tin reduction amount determined from Faraday constant)} × 100. Is greatly affected by the Sn concentration in the electrolyte. Figure 2 shows the effect of Sn concentration in the electrolyte on the cathode efficiency.

From FIG. 2, the cathode efficiency becomes 90% or more only when the Sn concentration in the electrolytic solution is 20 g / l or more, and the cathode efficiency becomes 100% when the Sn concentration is 45 g / l or more. Therefore, the Sn concentration in the electrolytic solution is preferably in the range of 20 to 45 g / l. The Sn concentration in the electrolytic solution can be adjusted by adding a tin-containing solid content. In the electrolytic reduction treatment, it is preferable to perform electrolysis in an electrolytic bath by using the above alkali dissolution treatment liquid as an electrolytic solution, the cathode as a metal tin plate, and the anode as a steel plate. It is preferable that the electrolytic bath and the alkaline dissolving bath are connected by piping so that the electrolytic solution can be circulated by a pump or the like. Regarding the circulation of the electrolytic solution, it is preferable to constantly monitor the concentration in the electrolytic solution and adjust the supply amount of a new electrolytic solution based on the result. Further, it is preferable to install a heater in the electrolytic cell for adjusting the temperature of the electrolytic solution. The electrolyte temperature is preferably 75 to 85 ° C.

Further, the electrolytic reduction treatment with the alkali dissolution treatment liquid is a wet method, so that the work environment is less likely to be deteriorated due to the volatilization of dust and the like. Further, the purity of tin that is reduced and recovered by the electrolytic reduction treatment is 99.9% or more, and it can be reused as an anode for electrotin plating.

[0029]

[Example] (Example 1) Sludge produced in a plating bath by halogen method electrotin plating was dumped out and subjected to water leaching treatment with hot water at 60 ° C. This warm water was adjusted to pH 3.4 by adding NaOH. In the water leaching process, H ₂ O ₂ was added as an oxidant for oxidizing iron ions.

After the water leaching treatment, the sludge-containing liquid was subjected to a solid-liquid separation treatment with a filter press to separate it into a solid content rich in iron and a filtrate rich in tin. Then, an aqueous NaOH solution was added to the obtained filtrate to adjust the pH shown in Table 1. After adjusting the pH, the aqueous solution containing the solid content was subjected to solid-liquid separation by a filter press. To the obtained tin-containing solid content of 930 kg, an aqueous solution of sodium hydroxide was added and alkali dissolution treatment was performed.
The concentration was 30 g / l. After that, the alkali dissolution treatment liquid was transferred to an electrolytic bath, and an electrolytic reduction treatment was performed at a temperature of the electrolyte of 80 ° C. using a metal tin plate as the cathode and a steel plate as the anode.

Filtrate at each stage, tin concentration in solid content,
The iron concentration and the recovery rate of metallic tin were measured, and the results are shown in Table 1. From Table 1, it is understood that the lower the pH at the time of water leaching, the higher the recovery rate and the better. The obtained metal tin was reused as an anode for plating treatment. As a comparative example,
After the tin-containing solid content was dried, it was melted together with graphite in a reducing furnace, the melting temperature was adjusted to separate iron, and molten tin was tapped. The molten tin discharged was cast into metallic tin. The recovery rate of metallic tin is 64 with respect to the total amount of tin in sludge (290 kg).
%Met.

[0032]

[Table 1]

In the example of the present invention, although the concentration of Fe in the filtrate obtained after the water leaching process was high, the purity of the metal tin recovered was high, and the tin recovery rate was 83% .
The yield of tin is higher than that of the comparative example by 20 % or more. Furthermore, the recovery of metallic tin from the tin-containing solids in the comparative example was performed at high temperature (
The method of the present invention has the effect of being wet and at a low temperature of 100 ° C. or less and having good operability, as compared with being dry at about 1000 ° C.).

[0034]

Industrial Applicability According to the present invention, it is possible to recover tin from sludge with a high yield, and it is possible to effectively use resources without worrying about environmental pollution, and to achieve a marked industrial effect. In addition, according to the present invention, sludge can be easily treated in a facility attached to an electric tin plating line, and there is no need to worry about storage of sludge and environmental pollution.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a sludge treatment flow suitable for carrying out the present invention.

FIG. 2 is a graph showing the relationship between Sn concentration in an electrolytic solution and cathode efficiency in electrolytic reduction treatment.

FIG. 3 is an explanatory diagram showing a conventional sludge treatment flow.

FIG. 4 is an explanatory diagram showing a flow of conventional tin plating sludge treatment.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Fuyuhiko Ishikawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Inside the Chiba Works (56) Reference JP-A-63-277782 (JP, A) JP-A-SHO 62-40400 (JP, A) JP 57-70242 (JP, A) JP 11-335900 (JP, A) JP 11-269699 (JP, A) JP 10-72693 (JP, A) JP-A-9-103790 (JP, A) JP-A-9-67699 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C25D 21/18

Claims (2)

(57) [Claims] 1. A method for treating sludge generated during electroplating of metal tin on a steel sheet by halogen method electrotin plating, wherein the sludge has a pH range of 1.0 to less than 4.
In after the water leach, subjected to solid-liquid separation process, and the obtained filtrate was pH adjusted, subjected to solid-liquid separation process, subjected to alkaline lysis process resulting solid was the alkali dissolution treatment A method for treating sludge, which comprises recovering metallic tin by performing electrolytic reduction treatment using the solution as an electrolytic solution. 2. The sludge treatment method according to claim 1, wherein the electrolytic reduction treatment is carried out at an Sn concentration in the electrolytic solution in the range of 20 to 45 g / l.